Induction of cytochrome P450 1A is required for circulation failure and edema by 2,3,7,8-tetrachlorodibenzo-p-dioxin in zebrafish

The mechanism of toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is thought to result from changes in gene expression via the aryl hydrocarbon receptor (AHR). The induction of cytochrome P450 1A (CYP1A) in various organs is a cardinal effect of TCDD. However, whether CYP1A is involved in endpoints of TCDD toxicity is controversial. We investigated the role of CYP1A in TCDD-induced developmental toxicities using gene knock-down with morpholino antisense oligos. Exposure of zebrafish embryos to TCDD, at concentrations eliciting the hallmark endpoints of developmental toxicity, induced CYP1A in the heart and vascular endothelium throughout the body. This induction by TCDD was markedly inhibited by morpholinos to zebrafish arylhydrocarbon receptor 2 (zfAHR2-MO) and to zebrafish CYP1A (zfCYP1A-MO). The zfAHR2-MO but not the zfCYP1A-MO inhibited zfCYP1A mRNA expression, indicating the specificities of these morpholinos. Injection of either zfAHR2-MO or zfCYP1A-MO blocked the representative signs of TCDD developmental toxicity in zebrafish, pericardial edema and trunk circulation failure. The morpholinos appeared do not affect normal development in TCDD-untreated embryos. These results suggest a mediatory role of zfCYP1A induction through zfAHR2 activation in causing circulation failure by TCDD in zebrafish. This is the first molecular evidence demonstrating an essential requirement for CYP1A induction in TCDD-evoked developmental toxicities in any vertebrate species.     

Polymorphisms of interferon-inducible genes OAS-1 and MxA associated with SARS in the Vietnamese population

We hypothesized that host antiviral genes induced by type I interferons might affect the natural course of severe acute respiratory syndrome (SARS). We analyzed single nucleotide polymorphisms (SNPs) of 2',5'-oligoadenylate synthetase 1 (OAS-1), myxovirus resistance-A (MxA), and double-stranded RNA-dependent protein kinase in 44 Vietnamese SARS patients with 103 controls. The G-allele of non-synonymous A/G SNP in exon 3 of OAS-1 gene showed association with SARS (p=0.0090). The G-allele in exon 3 of OAS-1 and the one in exon 6 were in strong linkage disequilibrium and both of them were associated with SARS infection. The GG genotype and G-allele of G/T SNP at position -88 in the MxA gene promoter were found more frequently in hypoxemic group than in non-hypoxemic group of SARS (p=0.0195). Our findings suggest that polymorphisms of two IFN-inducible genes OAS-1 and MxA might affect susceptibility to the disease and progression of SARS at each level.     

Enhanced plasma ghrelin levels in rats with streptozotocin-induced diabetes

Human saliva, which contains nitrite, is normally mixed with gastric juice, which contains ascorbic acid (AA). When saliva was mixed with an acidic buffer in the presence of 0.1 mM AA, rapid nitric oxide formation and oxygen uptake were observed. The oxygen uptake was due to the oxidation of nitric oxide, which was formed by AA-dependent reduction of nitrite under acidic conditions, by molecular oxygen. A salivary component SCN⁻ enhanced the nitric oxide formation and oxygen uptake by the AA/nitrite system. The oxygen uptake by the AA/nitrite/SCN⁻ system was also observed in an acidic buffer solution. These results suggest that oxygen is normally taken up in the stomach when saliva and gastric juice are mixed.     

Determination of naringin and naringenin in human plasma by high-performance liquid chromatography

An HPLC method for determining a flavonoid, naringin, and its metabolite, naringenin, in human plasma is presented for application to the pharmacokinetic study of naringin. Isocratic reversed-phase HPLC was employed for the quantitative analysis by using genistin (for naringin) or daidzein (for naringenin) as an internal standard and solid-phase extraction using a Sep-Pak t C₁₈ cartridge. For the determination, HPLC was carried out using an Inertsil ODS-2 column (250x4.6 m I.D., 5 μm particle size). The mobile phases were acetonitrile-0.1 M ammonium acetate solution (20:80, v/v; pH 7.1) for naringin and acetonitrile-0.1 M ammonium acetate solution-acetic acid (30:69:1, v/v; pH 4.9) for naringenin. The flow-rate was 1 ml min⁻¹. The analyses were performed by monitoring the wavelength of maximum UV absorbance at 280 nm for naringin and at 292 nm for naringenin. The detection limits on-column were about 0.2 ng for the two flavonoids.     

Crystal structure of inorganic pyrophosphatase from Thermus thermophilus.

The 3-dimensional structure of inorganic pyrophosphatase from Thermus thermophilus (T-PPase) has been determined by X-ray diffraction at 2.0 A resolution and refined to R = 15.3%. The structure consists of an antiparallel closed beta-sheet and 2 alpha-helices and resembles that of the yeast enzyme in spite of the large difference in size (174 and 286 residues, respectively), little sequence similarity beyond the active center (about 20%), and different oligomeric organization (hexameric and dimeric, respectively). The similarity of the polypeptide folding in the 2 PPases provides a very strong argument in favor of an evolutionary relationship between the yeast and bacterial enzymes. The same Greek-key topology of the 5-stranded beta-barrel was found in the OB-fold proteins, the bacteriophage gene-5 DNA-binding protein, toxic-shock syndrome toxin-1, and the major cold-shock protein of Bacillus subtilis. Moreover, all known nucleotide-binding sites in these proteins are located on the same side of the beta-barrel as the active center in T-PPase. Analysis of the active center of T-PPase revealed 17 residues of potential functional importance, 16 of which are strictly conserved in all sequences of soluble PPases. Their possible role in the catalytic mechanism is discussed on the basis of the present crystal structure and with respect to site-directed mutagenesis studies on the Escherichia coli enzyme. The observed oligomeric organization of T-PPase allows us to suggest a possible mechanism for the allosteric regulation of hexameric PPases.     

Plant reproductive intervals and pollinators in the aseasonal tropics: a new model

What factors determine reproductive intervals and modes of pollination in plants of the aseasonal tropics? To answer this general question, we present a new explanation for some community patterns of plant reproductive intervals and pollinators observed in a lowland dipterocarp forest in Sarawak, Malaysia, using a mathematical model featuring different display effects for different types of pollinators. Predictions from the model matched with the following observed patterns: (i) flowering intervals were different among forest strata (forest floor < understorey < canopy < subcanopy and emergent), and not in the exact order of stratum height; (ii) among generalist pollinators, the proportion of social foragers was maximum in intermediate forest stratum; and (iii) plants pollinated by specialist pollinators were found on the forest floor and in gaps.